(T2AG3)n telomeric sequence hybridization suggestive of centric fusion in karyotype marsupials evolution

It has been suggested that the karyotype of the marsupials derived from a low diploid number (2n = 14) which originated, through fissions of biarmed chromosomes, the karyotypes with a higher 2n. The telomeric sequence (T(2)AG(3))(n) was in situ hybridized to the chromosomes of Gracilinanus microtarsus and G. emiliae, Micoureus demerarae and Marmosa murina, species with 2n = 14, in Monodelphis sp., M. domestica, M. kunsi and M. brevicaudata with 2n = 18, and Lutreolina crassicaudata, Didelphis albiventris, Chironectes minimus, Philander opossum and P. frenata, all of them with 2n = 22. The probe hybridization occurred in the telomeric regions of both arms, short and long, of all chromosomes of the complement of all individuals of all species analysed. However, in some pairs of the karyotypes of Gracilinanus microtarsus and Micoureus demerarae (with 2n = 14), and in Monodelphis sp., M. domestica, M. kunsi and M. brevicaudata (2n = 18) ectopic signs of hybridization were detected proximal to the centromeres, suggesting the retention of this telomeric sequence in the centromeric regions of some chromosomes of these species. Based on these results, it is proposed that the karyotype of marsupials evolved from a 2n = 22 to a 2n = 14, by means of chromosomal fusions.